Causes and Prevention of Diplopia After Refractive Surgery

Transcription

1 Causes and Prevention of Diplopia After Refractive Surgery Burton J. Kushner, M.D. ABSTRACT Background and Purpose: To describe the decompensation of strabismus or the occurrence of persistent diplopia after refractive surgery, list different causes for these complications, outline risk stratification for their occurrence, and outline screening techniques for their prevention. Patients and Methods: A retrospective review of patients examined and treated for persistent diplopia or decompensated strabismus after refractive surgery. Results: The review identified thirty- seven patients. The etiologies of the complications were either due to technical problems or judgment errors with respect to planning. This latter category included the failure to recognize prior need of prisms, predictable aniseikonia, the surgical creation of monovision, and improper control of accommodation in strabismic patients. From this series recommended screening criteria are outlined. Conclusions: Decompensation of strabismus or persistent diplopia can occur after refractive surgery. These complications can be minimized with careful attention to the identification of risks preoperatively. INTRODUCTION In the year 2001, it was estimated that 1.5 million people worldwide undergo a laser- assisted in situ keratomileusis (LASIK) annually, and that number is steadily increasing. 1 Although refractive surgery has a low complication rate and is generally successful, there are reports of decompensation of strabismus and / or persistent diplopia after refractive surgery In 2003 Lionel Kowal and I reported a series of twenty- eight patients who experienced one or both of these complications after refractive surgery. 10 The purpose of this article is to report my From the Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, Wisconsin. Requests for reprints should be addressed to: Burton J. Kushner, M.D., Dept. of Ophthalmology and Visual Sciences, Univ. of Wisconsin, 2870 University Ave., Suite 206, Madison, WI 53705; e- mail: bkushner@wisc.edu Presented as part of a Symposium at the Joint Meeting of the American Orthoptic Council, the American Association of Certified Orthoptists, and the American Academy of Ophthalmology, New Orleans, Louisiana, November 11, Board of Regents of the University of Wisconsin System, American Orthoptic Journal, Volume 58, 2008, ISSN X, E-ISSN American Orthoptic Journal 39

2 SYMPOSIUM: ADULT STRABISMUS continued experience with these complications in this patient population and to outline risk stratification and screening techniques to prevent their occurrence. METHODS A retrospective review was carried out of all patients seen by me between January 1, 1987, and June 30, 2007, who experienced decompensation of their strabismus or persistent monocular or binocular diplopia after undergoing refractive surgery. In addition this series includes the patients seen by Dr. Kowal that were included in our prior joint publication, subject to the same inclusion criteria. 10 All patients underwent a complete ophthalmologic evaluation that included a detailed ocular motility and / or orthoptic exam with particular attention to sensory status. When appropriate, records were reviewed from the ophthalmologist who performed the refractive surgery or from ophthalmologists or optometrists who cared for the patient in earlier years. RESULTS The review identified thirty- seven patients who met the inclusion criteria. The gender distribution was eighteen males and nineteen females. Their ages ranged from twenty years to fifty- seven years (mean ± SD, 38.4 ± 9.3). A list of the different causes for the diplopia or decompensation of strabismus is shown in Table 1. In general, I was able to divide the etiology into two broad categories: technical problems and judgment errors in surgical planning. Technical Problems Technical problems accounted for the decompensation of strabismus or development of diplopia in fourteen patients in this series. The only three patients in this series who experienced monocular diplopia were ones who had undergone LASIK. In one there was scarring due to a buttonhole of the corneal flap, in another the ablation zone was too small, and in a third the treatment zone was decentered. Surgical undercorrections seemed to be more of a problem in hyperopic patients than myopic patients, which was problematic in some patients with accommodative esotropia. In general, more technical problems occurred with radial keratotomy (RK) than with LASIK or photorefractive keratectomy (PRK). When I first began seeing patients with diplopia after RK, I mused that if spectacles had been invented after refractive surgery, a tabloid headline might read: Simple inexpensive optical device replaces costly, painful, risky, unpredictable surgical procedure! I believe the inventor of spectacles would have been a candidate for the Nobel Prize! Judgment Errors in Surgical Planning Twenty- three patients experienced the decompensation of strabismus or persistent diplopia as a result of errors in judgment with respect to surgical planning. These included patients who had needed prisms in their spectacles before refractive surgery, and the need of prisms was unknown either to the doctor, the patient, or both at the time of refractive surgery. In two patients there was substantial anisometropia that did not result in aniseikonia when the patient was in spectacles. To the extent that Knapp s rule is correct, such patients might be expected to experience aniseikonia if their anisometropia is corrected at the corneal plane (as occurs after refractive surgery). 10 This was the cause of persistent diplopia in two patients. One patient had an accommodative esotropia and was wearing a progressive (no- line) 40 Volume 58, 2008

3 KUSHNER TABLE 1 ETIOLOGY OF DIPLOPIA IN THIRTY-SEVEN PATIENTS Etiology No. of Patients Technical problems (N=14) Scarring 1 Ablation zone too small 1 Decentered ablation 1 Astigmatism axis or power change 2 Undercorrected hyperopia with accommodative esotropia 3 Undercorrected hyperopia with anisometropic exotropia 1 Unplanned monovision 2 Overcorrection Induced aniseikonia 1 Overcorrected myopia with esotropia 2 Judgment error with respect to planning (N=23) Prior prism 5 Predictable aniseikonia 2 Planned monovision Fixation switch diplopia 4 Intermittent strabismus, unstable fusion 3 Fourth nerve palsy 2 Incorrect Targeted Outcome Residual accommodation in esotrope with high AC / A 1 Intermittent exotropia in over- minus lenses 2 Difference between absolute and manifest hyperopia 1 Prior undercorrected hyperopia and exotropia 2 Unrecognized no line bifocal and esotropia 1 bifocal to control a preoperative larger near esotropic deviation. The existence of the bifocal and the need thereof was not recognized by the refractive surgeon, and this patient had a persistent esotropia at near fixation after refractive surgery. Previous reports have shown that monovision (optically correcting one eye for distance and the other eye for near) can cause problems in patients with strabismus. 11 Monovision was the cause of decompensation of strabismus or persistent diplopia in eleven of the thirty- seven patients. In two of them, the postoperative monovision was unplanned and was a result of a surgical undercorrection of a myopic refractive error in one eye of each of two patients. These patients are listed in Table 1 under Technical Problems. In the other nine patients, the postoperative monovision was part of the surgical planning, and they are therefore listed in the section on Judgment Errors. Monovision can cause problems in strabismus patients via three different mechanisms. Some patients with strabismus and a strong fixation preference experience fixation switch diplopia the moment they change fixation to their nondominant eye. 12 In these patients, a preoperative trial with monovision will identify them as being at high risk for diplopia after refractive surgery that creates monovision. Another group of patients includes those with intermittent strabismus and unstable fusion such as occurs in intermittent exotropia. In these patients, the unequal visual input to the two eyes can destabilize the alignment and result in a deterioration of the strabismus over time. 12,13 Finally, there American Orthoptic Journal 41

4 SYMPOSIUM: ADULT STRABISMUS seems to be a group of patients with paretic strabismus (most commonly fourth nerve palsy) who lose control after they are put in monovision correction. It has been speculated that this occurs because they are at times fixing with the paretic eye when experiencing monovision, and thus manifesting a secondary deviation. This exceeds their habitual fusional needs and overpowers their fusional reserve. 11 The final group of patients were those in whom the surgeon attained the targeted outcome refraction; however, that refractive error was not optimal for controlling the patient s strabismus. This occurred because the relationship between accommodation and convergence is crucial to managing patients with esotropia and exotropia. For example, patients with intermittent exotropia who need overcorrecting minus lenses to control the deviation, or patients with hyperopic intermittent exotropia who are intentionally wearing less than their full hyperopic refractive error to control the deviation, may experience decompensation if the refractive surgery targets their cycloplegic refractive error. In all thirty- seven patients, the diplopia or the recurrent strabismic deviation persisted until some optical or surgical intervention was carried out to address the underlying problem. Spontaneous resolution was an exclusion criterion for this study. COMMENT Decompensation of preexisting strabismus or persistent diplopia can occur after refractive surgery. The causative mechanisms include technical problems and errors in judgment with respect to planning. In our prior report on this subject, Dr. Kowal and I outlined some screening criteria and risk stratification for the prevention of these complications. 10 I feel these guidelines are still useful and would have identified all the patients in this series as being at risk for this postoperative complication, with the exception of those in whom technical problems were causative. These guidelines are repeated here with minor modification in Table 2. There are three different refraction values listed for hyperopic patients. For the manifest refraction, the least plus correction needed for threshold acuity is the absolute hyperopia, and the most plus correction accepted for threshold acuity equals the target hyperopia. The difference between the target hyperopia (maximum manifest plus accepted) and the cycloplegic refraction is the latent hyperopia. To understand the necessity for these multiple values, one must realize that hyperopia is not the inverse of myopia. Myopia can be viewed as a fixed value, whereas hyperopia can be thought of as a moving target. As will be seen in the risk stratification that follows, substantial differences between these values for a given hyperopic patient can be a warning sign of potential postoperative difficulties. Low Risk Patients are at low risk if they meet these criteria: no history of strabismus or diplopia, no prisms currently needed in their spectacles, myopia, less than 4 D of anisometropia, orthophoria or a trivial phoria, and current spectacles, manifest refraction, and cycloplegic refraction all within 0.5 D of each other. Patients are also low risk if they have a history of strabismus (including prior surgery) but have a good fusional range while wearing their absolute hyperopic or proper myopic correction. Moderate Risk Any patients who fail any inclusion criteria for the low risk category should be thought of as being at least at moderate risk. These patients should undergo the 42 Volume 58, 2008

5 KUSHNER TABLE 2 PREOPERATIVE SCREENING CRITERIA Preoperative Minimal Screening Criteria History Check spectacles for prisms and no- line bifocal Cover testing distance and near Refraction Manifest Cycloplegic Additional tests for moderate risks Fusional amplitudes: divergence and convergence Optical trial of monovision (spectacles or contact lenses) Trial with neutralizing prisms Comments Strabismus; diplopia; prism in spectacles; the need of bifocals, history of prior patching, surgery, or orthoptic exercises Performed while patient wears targeted optical correction Myopes: least minus for threshold acuity, Hyperopes: least plus for threshold acuity = absolute hyperopia, most plus accepted = target Difference between manifest maximum plus and cycloplegic = latent hyperopia If history or findings of diplopia, strabismus, prisms in spectacles, or a moderate phoria Perform if monovision is desired and there is a substantial phoria, prisms in spectacles, or history of strabismus If patient wears prisms in spectacles. appropriate additional tests listed in Table 2. If a strabismic patient desires monovision, a contact lens or spectacle trial to achieve monovision should be performed to assess the patient s response. In my experience, the presence of diplopia during such a trial indicates high risk and may be a contraindication to postoperative monovision; however, the absence of diplopia does not preclude complications from monovision. These patients are still at moderate risk for late decompensation for the previously mentioned reasons. Similarly, if a patient wears prisms in their spectacles, a preoperative trial with spectacles without prisms would indicate high risk if diplopia occurs immediately. Depending on the duration of the trial, patients may still be at moderate risk for symptoms even if they were not symptomatic with the contact lens trial. Refractive surgery is less precise for hyperopia than myopia. As such, patients with accommodative esotropia and poor fusional reserves (< 5 Δ ) have a moderate risk of postoperative diplopia. Patients with more than 2 D of latent hyperopia (the difference between the most plus power accepted for threshold vision and the cycloplegic refraction) may be at risk for late occurring diplopia, because the latent hyperopia will become more manifest with time. High Risk Any moderate risk patient should be considered high risk if he / she fails the additional testing called for in Table 2. Patients with more than 4 D of anisometropia and good fusion with spectacles are at high risk for aniseikonia with refractive surgery. A preoperative trial with a contact lens can be useful to determine how patients would respond to correction of the refractive error at the corneal plane. Finally, patients should be considered at high risk if they have accommodative esotropia and need substantially more plus correction than their absolute hyperopia to control their deviation. American Orthoptic Journal 43

6 SYMPOSIUM: ADULT STRABISMUS CONCLUSION Diplopia or decompensation of strabismus after refractive surgery can be disconcerting. Proper attention to risk stratification and screening guidelines can minimize these complications. REFERENCES 1. Melki S, Azar D: LASIK complications: Etiology, management, and prevention. Surv Ophthalmol 2001; 48: Davis E, Hardton D, Lindstom R: LASIK complications. Int Ophthalmol Clin 2000; 40: Marmer R: Ocular deviation induced by radial keratectomy. Ann Ophthalmol 1987; 19: Mandava N, Donnenfeld ED, Owens PL, Kelly HS, Haight DH: Ocular deviations following excimer laser photorefractive keratectomy. J Cataract Refract Surg 1996; 22: Zwaan J: Strabismus induced by radial keratotomy. Military Medicine 1996; 161: Schuler E, Silverberg M, Beade P, Moadel K: Decompensated strabismus after laser in situ keratomileusis. J Cataract Refract Surg 1999; 25: Kim SK, Lee JB, Han SH, Kim EK: Ocular deviation after unilateral laser in situ keratomileusis. Yonsei Med J 2000; 41: Holland D, Amm M, de Decker W: Persisting diplopia after bilateral laser in situ keratomileusis. J Cataract Refract Surg 2000; 26: Kowal L: Refractive surgery and diplopia. Clin Exp Ophthalmol 2000; 28: Kushner BJ, Kowal L: Diplopia after refractive surgery: Occurrence and prevention. Arch Ophthalmol 2003; 121: Kushner BJ, West C: Monovision may be detrimental to patients with strabismus. In: At the Crossings. Pediatric Ophthalmology and Strabismus. Proceedings of the 52nd Annual Symposium of the New Orleans Academy of Ophthalmology. Balkan RJ, Ellis GS, Eustis HS, eds. The Hague: Kugler Publications; pp Kushner BJ: Fixation switch diplopia. Arch Ophthalmol 1995; 113: Jampolsky AJ: Unequal vision inputs and strabismus management: A comparison of human and animal strabismus. In: Symposium on Strabismus: Transactions of the New Orleans Academy of Ophthalmology. St. Louis: CV Mosby Co.; pp Key words: strabismus, diplopia, LASIK, refractive surgery, monovision Continuing Education Credit Orthoptists wishing to earn American Orthoptic Council approved continuing education credits may earn 5 hours of credit by completing a self-study test based on the articles contained in the American Orthoptic Journal. Allied Health Personnel in Ophthalmology may earn 4 hours of JCAHPO approved continuing education credit upon successful completion of the self-test. Information regarding the test may be obtained by sending an request to: Jason DeBoer, Managing Editor, jwdeboer@wisc.edu 44 Volume 58, 2008